JP2011513685A - Heat exchanger for heating products sensitive to temperature and residence time - Google Patents

Abstract

  The present invention relates to a tube bundle heat exchanger for heat transfer in a temperature sensitive and / or polymerisable medium. In the configuration of the invention, a tube bundle is arranged in a housing (4) with one or more product outlets (8) and one or more product inlets (1), and within the tubes of the tube bundles. A plurality of push rods (7, 10, 12, 15) are arranged respectively, and at least one heat exchanger hood of the tube bundle heat exchanger is pushed away to reduce the volume filled with the product (3) Is filled with.

Description

The present invention relates to heat exchangers for products that are temperature sensitive, i.e. temperature sensitive and / or polymerisable.

From the literature, many different embodiments of heat exchangers are known. That is, for short residence times, for example, plate-type heat exchangers or micro heat exchanger type heat exchangers are mentioned. However, these heat exchangers have the disadvantage that they are only suitable for low viscosity products due to the narrow flow gap. In the case of high viscosity products, the pressure drop due to these heat exchangers can be very high. In the case of products that tend to polymerize, such as monomers or polymer syrups that still contain monomers, there is a risk that the monomers will polymerize in the heat exchanger during operation or at rest. Removing completely polymerized syrup from a plate-type heat exchanger or micro heat exchanger is a very laborious if not impossible. For high viscosities, in particular several Pas and high pressures, in particular pressures higher than 10 bar, plate-type heat exchangers are not conceivable, based on the production method and the forces generated.

  U.S. Pat. No. 1,916,907 describes a tube bundle heat exchanger with a pusher that is spirally grooved in the tube. A particularly effective heat transfer is achieved by the spiral flow. However, the flow of the medium to be tempered inside the drainage tube causes additional pressure loss and additional residence time, which can be detrimental to the product. Furthermore, based on a complex structure, the result is high costs, poor disassembly potential and difficult discharge possibilities.

  German Utility Model No. 8712815 (VIA Gesellschaft fuer Verfahrenstechnik) describes a tube bundle heat exchanger for use in a compressed air dryer. The displacement body introduced into the pipe again consists of a pipe for reasons of material saving, which pipe is closed on the inflow side. The pusher tube may have a knurled surface. However, this structure, which was not developed for a temperature sensitive product, has a large product filled capacity. This is because the bottom with very small hold-up is not used and the displacement rod is not closed down. Furthermore, the push-out tube is not removable. This is a major disadvantage for temperature sensitive polymers.

  German Utility Model No. 8903349 (VIA Gesellschaft fuer Verfahrenstechnik) describes a tube bundle heat exchanger used in particular for compressed air dryers. In order to make the heat transfer medium flow through the device as uniformly as possible, a sieve plate is arranged in the device. This sieving plate causes a uniform flow of the tube. However, since this tube bundle heat exchanger or tube bundle heat exchanger does not require gentle heat transfer, no special requirements are imposed on the cross section of the displacement rod, and the displacement hood or flatness with minimal hold-up is not imposed. The bottom is not required. Furthermore, the push rod is not removable.

  Heat exchangers that exhibit only a slight pressure drop even in high viscosity products are often, for example, tube bundle type heat exchangers. In this configuration, the product flows through a plurality of tubes arranged in parallel. However, the disadvantage in this case is that the tube bundle heat exchanger usually has only a small specific heat exchange surface (spezifische Waermeaustauschflaeche). This specific heat exchange surface is defined as the ratio of the heat exchange area to the volume in the tube filled with product. Based on a small specific heat exchange area, generally a large heat exchanger and thus a heat exchanger with a large hold-up in the tube is required. Therefore, the residence time is very long in the tube bundle heat exchanger.

Problem In view of the known prior art described above, the problem arises of developing a heat exchanger that minimizes the residence time for products that are desired to be heated or cooled in the heat exchanger. It is further desirable that the heat exchanger be configured so that both low and high viscosity products can be heated or cooled.

in this case,
・ Allows slight pressure drop at the same time as short residence time,
・ Easy to clean
・ Easy to manufacture
・ Easy to seal
Can be used for wide temperature, pressure and viscosity spectra
-A heat exchanger configuration that satisfactorily accepts the temperature difference between the product room and the heating or cooling room was required.

  This problem is solved by a tube bundle heat exchanger with a plurality of specially formed displacement rods in a product-filled tube. These displacement rods occupy more than 40% of the volume present in the tube, preferably more than 50% of the volume present in the tube, very particularly preferably of the volume present in the tube. It is formed to occupy a volume greater than 60%. In order to keep the product-filled volume in the device small, it is advantageous if one or more pushers are arranged in the heat exchanger hood of the device or at least one flat bottom is used. .

It is the schematic which shows one Embodiment of the tube bundle heat exchanger by this invention. It is a top view of the push rod in a heat exchanger pipe | tube. It is sectional drawing of the push rod along the AB line | wire of FIG. It is the schematic of the displacement rod shown in FIG. It is sectional drawing of the push rod along the AB line of FIG. It is the schematic of the displacement rod shown in FIG. It is the schematic which shows the heat exchanger hood by which the side facing the heat exchanger pipe | tube is formed in cone shape. It is the schematic which shows another embodiment of the tube bundle heat exchanger by this invention provided with the flat bottom part.

1. Configuration of Tube Bundle Heat Exchanger Description The tube bundle heat exchanger comprises a housing 4 and a tube bundle. The tube bundle is formed from one or more tubes arranged approximately in parallel that are circulated by the product to be conditioned. The tubes may be arranged in alignment with each other, arranged offset from each other, or arranged to draw a plurality of hole circles concentric with each other. An approximately equal minimum tube spacing is advantageous, which results in a small volume 6 filled with product. In order to obtain a uniform flow of tubes and a slight dead zone in the bottom area, it is particularly advantageous if these tubes are arranged in a concentric circle.

  The product flows through these tubes and is heated or cooled through the tube jacket. A heating or cooling medium 5 flows through the jacket outside the tube. The tubes can in this case be passed by the heating or cooling medium 5 in the form of a crossflow, countercurrent or cocurrent flow with respect to the product stream. It is advantageous that the temperature adjustment is performed mainly in orthogonal / counterflow. This is because a small drive temperature difference between the temperature control medium, that is, the heating medium or cooling medium 5 and the product chamber 6 is sufficient. In order to be able to carry out the discharge easily, it is advantageous if the heat exchanger is passed by the product from above to below. In order to be able to vent the heating medium or the cooling medium 5 easily, it is advantageous if the heat exchanger is passed by the heating medium or the cooling medium 5 from below to above.

  At least one end of the tube bundle is surrounded by a bottom through which the product flows in or out. This bottom part may be formed as a heat exchanger hood 2 having a small wall thickness, or may be formed as a thick, but compact, flat, flat bottom part 17. The bottom preferably has a device flange so that it can be flanged to the heat exchanger body or removed again. The bottom may advantageously have a tube piece located on the axis through which the product can flow in or out. It is also conceivable that a plurality of tube pieces are arranged in the vicinity of the axis and the product flows out through these tube pieces. The bottom is advantageously formed such that the bottom can be heated or cooled by a temperature control medium, ie a heating medium or a cooling medium 5. However, electrical heating is also conceivable.

  It is also conceivable for the heat exchanger to be connected directly to another device, so that a corresponding bottom is not necessary on this connected side.

  For expansion compensation, a compensator can be inserted into the outer jacket as needed, thereby compensating for the thermal expansion difference between the tube bundle and the outer jacket.

Advantages The pressure drop in the heat exchange tube can be controlled by selecting an appropriate tube diameter for high viscosity products.

2. Configuration of displacement rod Description In order to reduce the volume of the product 6 in the heat exchanger tube and improve the heat transfer, displacement rods 7, 10, 12, 15 are introduced into the tube. The push-out rods 7, 10, 12, 15 can partially enter the heat exchanger hood 2. The push rods 7, 10, 12, and 15 are formed so as to push a volume larger than 40% of the volume in the heat exchanger tube. Advantageously, a volume greater than 60% of the empty volume of the tube is displaced by the displacement rods 7, 10, 12, 15. In order to obtain a compact structure of the heat exchanger or heat exchanger and at the same time keep the pressure drop small, it is advantageous if less than 95% of the volume is displaced. The outer contour of the displacement rods 7, 10, 12, 15 is the axis of the displacement rods 7, 10, 12, 15 in the tube in order to avoid a dead zone and obtain a uniform flow across the cross section of the heat exchanger tube. It is advantageous if it is designed to be centered. The product stream flows in the gap 11 between the displacement rods 7, 10, 12, 15 and the inner wall of the heat exchanger tube.

In order to center the displacement rods 7, 10, 12, 15 in the pipe with a defined gap, the displacement rods 7, 10, 12, 15 may be formed, for example, as follows:
A closed tube, closed hollow body or solid body 15 (closed on both sides) whose cross section has been deformed in its at least two partial areas 14, 16 along its axis for centering in the tube 9; FIG. 2, FIG. 5 and FIG. 6),
A closed tube, closed hollow body or solid body 15 (see FIGS. 3 and 4) with elements 13 mounted externally in at least two axial positions for centering within the tube ),
A plate that is displaced along the tube axis with the property of pushing away the volume.

  The displacement rods 7, 10, 12, 15 are preferably pushed into the tube 9, so that they can be removed again for cleaning and inspection purposes as required. Can do. The displacement rods 7, 10, 12, 15 may consist of a plurality of individual rods connected in series. It is also conceivable to use a hollow push rod. In that case, these displacement rods are filled with a medium that improves heat transport. For example, water may be included. Since water evaporates in the high temperature range and condenses in the low temperature range, heat is transported axially. It is also conceivable to additionally transfer heat using a heat carrier medium that flows through the displacement tube. Another possibility is to use an electrically heated displacement rod. Thereby, the specific heat transfer surface can be further enhanced and the residence time can be further reduced. It is also conceivable to use the combination of push rods listed above.

  The displacement rod advantageously forms a narrow cross section in the heated part of the tube, and in the inflow range, a cross-section expansion may be provided to reduce the pressure loss in the tube bottom region. .

Advantages The push-out rods 7, 10, 12, 15 reduce the product hold-up in the pipeline 6 and increase the specific heat exchange surface. The pressure drop that occurs through a tube bundle heat exchanger or tube bundle heat exchanger with push rods 7, 10, 12, 15 is greater than that of micro heat exchangers and plate heat exchangers with the same heat output and the same number of tubes. Is also small. In the case of micro and plate heat exchangers, the pressure drop is reduced to the level of tube bundle heat exchangers with displacement rods only by significantly increasing the number of tubes in these heat exchanger types. I can't. Small tube diameters and large numbers of tubes make cleaning or cleaning such heat exchangers extremely difficult.

  The residence time of the tube bundle heat exchanger with the displacement rod is of course shorter than in a tube bundle heat exchanger without the displacement rod of the same diameter. The residence time can only be adjusted to the same level as in the case of a tube bundle heat exchanger with a displacement rod, only with respect to empty tubes which have a significantly smaller diameter, but which are then formed to be very long.

3. Pusher in the heat exchanger hood Description In order to minimize the hold-up in the heat exchanger hood 2, the pusher 3 is incorporated in the heat exchanger hood 2. The heat exchanger hood 2 may also be heated or cooled. For centering, the heat exchanger hood 2 may have, for example, metal sheets or pins on the outside. In order to supply the liquid uniformly to the heat exchanger tube, it is advantageous if the side facing the heat exchanger tube is formed conically (see FIG. 7).

Advantages Reduction of residence time in the heat exchanger hood 2 and, in turn, reduction of product heat load.

4. Flat bottom The zone for the product inlet 1 and the product outlet 8 may be formed as a low volume head 17 with a notch (see FIG. 8). These notches have a residence time of the product at the bottom of 0.5 to 20 seconds, preferably 1.5 to 15 seconds at full load, and 1 to 40 seconds and advantageous at partial load. Is dimensioned to be 1.5 to 30 seconds. The notch can be made, for example, by turning or milling. The notch in the flat bottom portion may be formed in a conical shape.

5. Operating parameters Description Operating temperature T = -20 ° C to + 400 ° C;
Pressure P in the product chamber of the tube 6 and the heat exchanger hood 2 = −0.95 barg to +100 barg.

  The pressure in the chamber of the heat carrier 5 may be P = −0.95 bar to +50 barg. The temperature of the heat carrier medium 5 may be T = −20 ° C. to + 400 ° C.

  The heat carrier medium 5 can be supplied in liquid or vapor form. The heat exchanger described in the present invention is suitable for heating or cooling products having a viscosity of η = 0.1 mPas to 500 Pas. The residence time of the product in the heat exchanger may be 1 second to 300 seconds.

Advantages This heat exchanger allows a wide range of adjustments of temperature, pressure and viscosity.

Comparison between known prior art conventional heat exchangers and heat exchangers with annular gaps The following table shows the results of mass and energy balances and calculations of flow and heat transfer in tubes and annular gaps The results are summarized. The calculation of pressure loss is based on the analytical solution of the law of conservation of momentum (Impulserhaltungsgleichung) for a laminar flow pipe (Hagen-Poiseuille flow) or a laminar flow annular ring. Yes. The calculation of heat transfer is based on a semiempirisch Nusselt number relationship for laminar flow that is not hydrodynamically and thermally formed. Unless otherwise specified, the mass flow rate is 1000 kg / h, the residence time in the tube is 60 seconds, the temperature increase of the medium to be heated is 100K, and the logarithmic temperature difference between the heat carrier medium 5 and the medium to be heated is 30K. Assume. The previous two values can be combined to form a 3.33 quotient. As the material value, a thermal conductivity of 0.15 W / mK, a density of 1000 kg / m ³ , a specific heat capacity of 2.200 J / kgK and a constant kinematic viscosity of 1 Pas are used. That is, it starts from a Newtonian medium. Further, it is assumed that the heat transfer resistance on the heat carrier side and the pipe line resistance due to the pipe wall are negligible.

  Example A shows that in a conventional tube bundle heat exchanger or tube heat exchanger, very dense and long tubes are required to achieve the specified conditions. However, such tubes are extremely difficult to manufacture and cannot be substantially cleaned.

  Examples B and C show that short tubes are possible with short residence times (Case B) or with altered thermal conditions (Case C). In this case, however, the diameter of the tube is further reduced and the number of tubes is significantly increased.

  Examples D and E do show that relatively large residence times (Case D) or relatively high wall temperatures (relatively large log temperature difference; Case E) can be used to obtain relatively large tube diameters. ing. However, the benefits of good cleanability based on relatively large diameters are over-represented by extremely increased tube lengths that make fabrication very difficult and product quality degradation based on increased residence time and wall temperature. Compensated. Furthermore, the required space in the building of such a long device becomes a problem.

  Examples F and G show that a relatively small residence time (Case F) or altered thermal conditions (Case G) results in a relatively small tube diameter leading to an extremely large number of tubes. Such a high number of elaborate tubes cannot be produced considering that the tube bundle device must be designed for high pressures and temperatures.

  Furthermore, tube lengths that cannot be ignored make cleaning inside the device impossible.

  Example H shows that due to the increased tube number and shortened length, the reduced pressure drop does not result in a small tube diameter. Based on the high number of thin tubes having lengths that cannot be extremely short, again cleanability as well as manufacturability are virtually impossible.

Comparison of the design in the present invention (Example I) with a conventional tube bundle heat exchanger or tube bundle heat exchanger design (Examples A-H):
Example I exemplarily shows a design for a heat exchanger according to the invention with a displacement rod. In view of residence time, heat conditions and pressure drop, the heat exchanger according to the invention has a very large tube diameter compared to the conventional heat exchanger example (examples A-H), such as A large tube diameter ensures good cleanability. Furthermore, compared to Examples A, D and E, the tube length is limited, which allows for good manufacturability and cleanability and requires little space. Furthermore, since the number of tubes is smaller than those of Examples A-C and F-H, simple and inexpensive production is possible.

  The tube bundle heat exchanger according to the invention can be used particularly advantageously in the synthesis of polymers. This is because the effective heat transfer simultaneously with the short residence time results in the product not being overheated and thus preventing unwanted polymerization.

に基づき、３つの幾何学的形状量、つまり３つのジオメトリ量（ギャップ外径ｄ_ａ、ギャップ内径ｄｉ、管長Ｌ）のうちの２つのジオメトリ量が予め設定されると、第３のジオメトリ量を算出することができる。 Calculation method Heat balance in the pipe wall:

Based on the three geometric shapes amount, i.e. three geometries amount (the gap outside diameter d _a, gap inside diameter di, tube length L) when two geometry amount of is set in advance, the third geometry amount Can be calculated.

In this case, L is the tube length or the annular gap length, T is the residence time, d _a is the outer diameter of the annular gap or tube diameter, d _i is the inner diameter of the annular gap (tube: d _i = 0), [rho is the density, c _p is the specific heat capacity, [Delta] T _s is the temperature increase of the syrup, d _h is the hydraulic diameter, lambda is the thermal conductivity, [Delta] T _lg the heating medium 5 Logarithmic temperature difference from syrup.

を介して算出される。 The average Nusselt number Num is hydrodynamic and thermal for pipes according to Baehr / Stefan ("Waerme- und Stoffuebertragung", publisher Springer-Verlag Berlin, 1994, pages 381-382). Consider a good start (Anlauf):

Is calculated via

である。 In this case, Pr is the Prandtl number and X is the dimensionless length:

It is.

が成立する。 For the average Nusselt number in an annularly heated annular gap using K = di / da, further:

Is established.

が成立する。 The pressure drop in the annular gap or in the tube (K = 0) is based on Martin (“Waermeuebertrager”, publisher Georg Thieme Verlag Stuttgart, 1988, page 24):

Is established.

DESCRIPTION OF SYMBOLS 1 Pipe inlet 2 Heat exchanger hood 3 Push body 4 Heat exchanger housing 5 Heating medium and / or cooling medium surrounding a heat exchanger pipe 6 Product room in a heat exchanger pipe 7 Push rod in a pipe of a tube bundle 8 Product outlet 9 Heat Exchanger tube (schematic)
DESCRIPTION OF SYMBOLS 10 Displacement rod 11 Free volume between displacement rod and heat exchanger pipe 12 Displacement rod 13 Holder for centering displacement rod in heat exchanger 14 Centering range in partial range of displacement rod 15 Displacement rod 16 Displacement rod Centering range provided in the partial range 17 Low volum head

Claims (10)

  A tube bundle heat exchanger for heat transfer in a temperature sensitive and / or polymerisable medium with one or more product outlets (8) and one or more product inlets (1) A tube bundle is disposed in the housing (4), and a plurality of push rods (7, 10, 12, 15) are respectively disposed in the tubes of the tube bundle, and at least one heat exchanger of the tube bundle heat exchanger. Tube bundle heat exchanger, characterized in that the hood is filled with displacement bodies (3) to reduce the product-filled volume.   2. The tube bundle heat exchanger according to claim 1, wherein the push rod (7, 10, 12, 15) is formed to be removable for cleaning purposes.   2. The tube bundle heat exchanger according to claim 1, wherein the push rod (7, 10, 12, 15) has a cross section with a self-centering action.   2. The tube bundle heat exchanger according to claim 1, wherein the displacement rod (7, 10, 12, 15) occupies a volume of more than 40% of the volume of the tube.   2. The tube bundle heat exchanger according to claim 1, wherein the displacement rods (7, 10, 12, 15) occupy more than 50% of the volume of the tube.   2. The tube bundle heat exchanger according to claim 1, wherein the displacement rods (7, 10, 12, 15) occupy more than 60% of the volume of the tube.   2. The tube bundle heat exchanger according to claim 1, wherein the displacement rods (7, 10, 12, 15) occupy up to 95% of the volume of the tube.   Use of a tube bundle heat exchanger according to any one of claims 1 to 7 in the synthesis of polymers.   A tube bundle heat exchanger for heat transfer in a temperature sensitive and / or polymerisable medium with one or more product outlets (8) and one or more product inlets (1) A tube bundle is arranged in a substantially cylindrical housing (4), and a plurality of push rods (7, 10, 12, 15) are arranged in the tubes of the tube bundle, respectively, and at least one of the tube bundle heat exchangers. Tube bundle heat exchanger, characterized in that one bottom is formed as a flat bottom (17) to reduce the product-filled volume.   In a temperature-sensitive and / or polymerisable medium according to claim 9, wherein the residence time of the product in the notch provided in the flat bottom (17) is 0.5 to 40 seconds. Tube bundle heat exchanger for heat transfer.

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